HEVC (H.265) Encoding not available on Steam for Linux?

[falk4243]

Your system information

• Steam client version (build number or date): 1659369000 (regular and flatpak version)
• Distribution (e.g. Ubuntu): Debian testing
• Opted into Steam client beta?: No (doesn't help)
• Have you checked for system updates?: Yes

Please describe your issue in as much detail as possible:

HEVC (H.265) should be shown in the streaming stats when selecting the option in the mobile client, but only AVC (H.264) encoding seems to be available. HEVC encoding is supported by the system and works with Sunshine for example. It is a much better option for many AMD cards (where H.264 seems to have been an afterthought) and with the recently added VAAPI support (#4890) should run efficiently even at UHD.

Steps for reproducing this issue:

1. Enable HEVC streaming in the setting on Steam Play for Android or iOS.
2. Start the Steam Remote Play session from the device.
3. Take a look at the streaming stats.